Low-dielectric films, and manufacturion method thereof, and electronic component using it

ABSTRACT

While a fine porous diamond particle film has been known as a high heat resistant and low dielectric constant film and also has high mechanical strength and heat conductivity, and is expected as an insulating film for multi-layered wirings in semiconductor integrated circuit devices, it is insufficient in current-voltage characteristic and has not yet been put into practical use. According to the invention, by treating the fine porous diamond particle film with an aqueous solution of a salt of a metal such as barium and calcium, the carbonate or sulfate of which is insoluble or less soluble, and a hydrophobic agent such as hexamethyl disilazane or triethyl monochlolo silane, as well as a reinforcing agent containing one of dichlorotetramethyl disiloxane or dimethoxytetramethyl disiloxane, thereby capable of putting the dielectric breakdown voltage and the leak current within a specified range of a practical standard.

TECHNICAL FIELD

The present invention concerns a low dielectric constant thin film as aninsulating film of a porous structure in which fine diamond particlesare bonded, and a manufacturing method thereof, as well as an electronicpart such as a semiconductor integrated circuit device of highintegration degree and high speed operation type using the same.

BACKGROUND ART

Among semiconductor integrated circuit devices, particulary in super LSIdevices, delay of signals passing through wirings prepared in devicesgives rise to a significant problem along with lowering of powerconsumption as the wirings become finer and are more integrated.Particularly, in a high speed logic device, RC delay due to theresistance and the distribution capacity of wirings results in mostprominent subject and, among all it is necessary to use a material oflow dielectric constant for inter-wiring insulating materials in orderto decrease the distribution capacity.

Heretofore, as an insulating film in a semiconductor integrated circuit,a silica film (SiO₂), a tantalum oxide film (Ta₂O₅), an aluminum oxidefilm (Al₂O₃), a nitride film (Si₃N₄) and the like have been used and,particularly, as an insulating material between multlayer willing, anitride film and a silica film doped with an organic material orfluorine have been used or studied as the low dielectric constant film.Further, as an insulating film for further lowering the dielectricconstant, a fluororesin, a silica film formed by baking a foamingorganic silica film, a porous silica film formed by depositing finesilica particles, etc. have been studied.

On the other hand, since diamond is more excellent in the heatconductivity and the mechanical strength than other materials, this is amaterial suitable to heat dissipation for semiconductor devices of highintegration degree and large heat generation amount and has been studiedin recent years. For example, JP-A No. 6-97671 proposes a diamond filmof 5 Mm thickness by a film forming method such as a sputtering method,ion plating method or duster ion beam method. Further, JP-A No. 9-263488proposes a film forming method of scattering fine diamond particles on asubstrate and growing diamond crystals using them as nuclei by supplyingcarbon by a CVD (Chemical Vapor Deposition) method.

The present inventors have obtained a specific dielectric constant of2.72 by a fine diamond particle film of a porous structure as alreadydisclosed in JP-A No. 2002-110870. Further, since fine diamond particlesdo not bond to each other, this results in a problem that the filmstrength is lowered and, in order to solve the problem, JP-A No.2002-289604 proposes a reinforcing method by crosslinking fine diamondparticles by means of a hexachlorodisiloxane treatment and it is shownthat a specific dielectric constant comparable with that in JP-A No.2002-110870 is obtained also by the treatment.

Further, the present inventors have reported that a specific dielectricconstant of 2.1 is obtained by heating and purifying fine diamondparticles in a mixed acid comprising sulfuric acid/nitric acid in theAcademic Conference (The 50th meeting of the Japan Society of AppliedPhysics and Related Societies, Pre-text No. 2, p913 (2003)).

Materials known so far as having low dielectric constant are listed inthe following table. TABLE 1 Name of material Specific dielectricconstant Silica (plasma CVD) 4.2-5.0 Fluorine-added silica 3.7 Diamond(single crystal) 5.68 Porous silica 1.5-2.5 Porous diamond 2.1-2.72Polyimide 3.0-3.5 Polytetrafluoroethylene 1.9 Gas 1Patent Document 1: JP-A No. 6-97671Patent Document 2: JP-A No. 9-263488Patent Document 3: JP-A No. 2002-110870Patent Document 4: JP-A No. 2002-289604Non-Patent Document 1: The 50th meeting of the Japan Society of AppliedPhysics and Related Societies, Pre-text No. 2, p913 (2003).

DISCLOSURE OF THE INVENTION

As described above, for further improvement of the integration degree,various studies have been made for obtaining materials having a specificdielectric constant being lower than 3.7 of the fluorine-added silica inthe table. Since the silica film per se comprises two kinds of atomselements of oxygen and silicon of high electronegativity, orientationpolarization remains and it is insufficient as the low dielectricconstant film, so that porous silica produced by a blowing method offine particles has been studied. However, they are insufficient in themechanical strength and have not yet been put to practical use. Further,while polytetrafluoroethylene as the fluororesin shown in the table hasa sufficient specific dielectric constant, this can not be used since asevere condition for the required heat resistance from 300° C. to 400°C. or higher in the semiconductor manufacturing process can not besatisfied While the polyimide is a heat resistant resin, it iscarbonized at 400° C. or higher and can not be used as well

As a result of further study, it has been found that the dielectricbreakdown voltage and insulation resistance are insufficient. This isbecause fine diamond particles contain amorphous carbon and graphite asimpurities as disclosed in JP-A No. 9-263488. Accordingly, while finediamond particles as coarse raw material are oxidized by a concentratedsulfuric acid or concentrated nitric acid to remove the impurities, thisis not yet sufficient and, while various methods such as increase of theoxidation temperature in the acid treatment has been studied, asufficiently high electric resistance value and a sufficiently highdielectric breakdown voltage have not yet been attained

In the course of such studies, the present inventors have found thatwhen fine diamond particles are treated with nitric acid, hydroxygroups, the carboxyl groups are formed on the surface and when they arefurther treated with sulfuric acid, sulfonic acid groups are furtherformed in addition to them. That is, it is considered that leak currentis caused and the dielectric breakdown voltage is not increased as wellby the water molecules having affinity with the hydrophilic groups andimpurities contained in a trace amount.

In addition, it has been found in a further study that electriccharacteristics were insufficient in which the dielectric breakdownvoltage was 0.58 MV/cm while it should be 1.0 MV/cm or higher and theleak current value as the reciprocal of the insulation resistance was10⁻⁴ A/cm² at 0.58 MV/cm while it should be 10⁻⁶ A/cm² or less as shownby the symbol “□” in FIG. 3

As a result of seeking for the cause by using infrared absorptionspectroscopy, it was found that when purified fine diamond particles aretreated with hexachlorodisiloxane, a broad absorption spectrum forhydroxy group increased at the wave number of 3400 cm⁻¹. It isconsidered that the hydroxy groups form HO—Si bonds due to thehydrolysis of unreacted Cl—Si bond of hexachlorodisiloxane with watercontent in air. In the course of the study described above, the presentinventors have found that the leak current was caused and the dielectricbreakdown voltage is not increased by the water molecules havingaffinity with the hydroxy groups and impurities contained in a traceamount.

Means for Solving the Problems

With an aim of suppressing generation of the hydrogen ions, the presentinventors have made an earnest study and, as a result, have developed anexcellent low dielectric constant film having at least fine diamondparticles and pores, in which the low dielectric constant film containsmetals of at least one of substance selected from the group consistingof various metal carbonate substances and various metal sulfatesubstances having a solubility to water at an ambient temperature of 1g/100 g or less, and have accomplished the present invention.

While most of metals except for some metals have electrical conductivityin the form of an element or metal ion dissolved in water, the metaloxides and water insoluble metal salts thereof are insulators. In theinvention, the dielectric breakdown voltage and the insulationresistance can be improved by rendering carboxyl groups and sulfonicgroups as ionic groups on the surface of fine diamond particlesnon-ionic, that is, non-water soluble or less water soluble. As a resultof study on the relation between the solubility to water and thedielectric breakdown voltage and insulation resistance of the metalcarbonate salt or the metal sulfate salt as the standard for the lesssolubilization, it has been found an effect of improving them when it isat least 1 g/100 g or less at an ambient temperature. It is preferredthat the water solubility of the metal carbonate or the metal sulfate islower and, further, it is more preferably 0.01 g/100 g or less, and theymay be also those known as insoluble.

The metal contained in the low dielectric constant film of the inventionis particularly preferably at least one member of the group consistingof calcium, strontium, barium, mercury, silver, lead and radium. Any ofthe carbonates of the metals has a solubility to water at an ambienttemperature of as low as 10⁻³ to 10⁻⁴ g/100 g and any of the sulfatesalts thereof has a solubility to water at an ambient temperature of aslow as from 0.6 to 10⁻⁶ g/100 g, which are suitable to the object of theinvention. Among the metals, calcium, barium, strontium and silver aremost preferred.

As a method of containing the metals into the low dielectric constantfilm, after forming a fine diamond particle film having pores by a knownmethod, a water soluble salt of a metal such as hydroxide, hydrochlorideand nitrate with the solubility to water of the metal carbonate or themetal sulfate of 0.1 g/100 g or less is selected and dissolved in water,the solution is impregnated into the pores of the fine diamond particlefilm and bonded with the carboxyl groups or/and sulfonic acid groupsbonded to the surface of fine diamond particles thereby rendering theminsoluble, followed by water washing and drying. Thus, a low dielectricconstant film subjected to the metal salt insolubilizing treatment ofthe invention can be obtained.

The treating solution used in the invention includes, for example, anaqueous solution of calcium hydroxide, calcium chloride, calciumnitrate, strontium chloride, strontium nitrate, barium hydroxide, bariumchloride, barium nitrate, mercury nitrate, silver nitrate, lead nitrate,and radium chloride. The concentration of the treating solution ispreferably between 0.1% by weight and 20% by weight. In a case where theconcentration is less than 0.1% by weight, the treating rate is slow,which is not preferred. In a case of the concentration of an aqueoussolution exceeding 20% by weight or a saturated concentration, itbecomes difficult to sufficiently wash excess salts intruded in thepores with water, which is not preferred

A fine diamond particle film having pores is prepared by coating anddrying an aqueous dispersion thereof to a single crystal siliconsubstrate drawn with a circuit or a glass substrate drawn with a circuitor a conductive film. The fine diamond particle film may be directlytreated with a treating solution of the invention described above or maybe treated after reinforcing the fine diamond particle film withhexachlorodisiloxane, etc. The treating method includes, for example, amethod of dipping a fine diamond particle film coated on a substrate inthe treating solution, a method of coating the treating solution at ahigh concentration of the invention on the film, or a method ofparticulating and spraying the treating solution of the invention on thefilm.

The invention also includes an electronic part having the low dielectricconstant film described above as a constituent element. As theelectronic part, a semiconductor integrated circuit of high integrationdegree and high speed operation type is most suitable but it may also bea usual semiconductor device or micro machine, or a usual capacitorhaving a low dielectric constant film containing the above-describedmetal and fine diamond particles and comprising pores (porous finediamond particle film).

The fine diamond particles used in the invention are preferably solidparticles with a particle size of from 1 nm to 1000 nm and purified to apurity of 95% or higher. Further, the porosity of the low dielectricconstant film of the invention is preferably from 40% to 70%.

Since the fine diamond particle film of the invention has pores, thesurface is naturally rough and it is can be densified. For this purpose,a known method such as an SOG (Spin on Glass) method, an SG (SilicateGlass) film method, a BPSG (Boron Phosphate SG) film method or a plasmaCVD method can be used.

Further, the present inventors have made an earnest study with an aim ofincreasing the electric resistance value, that is, lowering the leakcurrent and, as a result, have developed a low dielectric constant filmhaving at least fine diamond particles and pores, in which the surfaceof fine diamond particles have a group of the general formula —X whichis more hydrophobic than —OH (hydroxyl) group and have accomplished theinvention.

X of the general formula —X group is preferably hydrogen, fluorine, C₁to C₄ alkoxy group, phenoxy group, o-(n- or p-)alkylphenoxy group (inwhich the alkyl group: C₁ to C₄), OCOR, OCONRR′ or OSiR₃ [R and R′ eachrepresents hydrogen, C₁ to C₄ alkyl group, phenyl group, o-(m- orp-)alkylphenyl group].

A more preferred group in the general formula —X group in view of heatresistance represents fluorine or OSiR₃ [where R, R′ each representshydrogen, C₁ to C₄ alkyl group, phenyl group, O-(n- or p-)alkylphenylgroup], which can withstand a heat treatment condition at 300° C.

In the method of manufacturing the low dielectric constant film of theinvention, fine diamond particles are at first suspended in a solventsuch as water and coated and dried by a known method on a substrate toform a film and a hydrophobic agent is reacted in a gas state or aliquid state with active hydroxyl groups on the surface of the finediamond particles. As the reaction conditions in this case, temperature,concentration and time optimal to the reactivity with respectivehydrophobic agent and hydroxyl group are set.

The hydrophobic agent for forming OSiR₃ group as X in the generalformula —X group includes, for example, alkyl halogen silane such astimethyl monochlorosilane and dimethyl dichlorosilane, di(tetra, hexa orhepta) alkyl dilazane such as hexamethyl disilazane and heptamethyldilazane, dialkylaminotrialkyl silane such as dialkylaminotrimethylsilane, trialkylmonoalkoxy silane such as trimethylmonomethoxy silane,N,O-bis(trialkyl silyl)acetoamide such asN,O-bis(trimethylsilyl)acetoamide, N,O-bis(trialkylsilyl)tihalogenacetoamide such as N,O-bis(trimethylsilyl)trifluoro acetoamide,alkylsilyl imidazole such as trimethylsilyl imidazole andbutyldimethylsilyl imidazole, arylated alkyl monohalogen silane such astriphenyl monochloro silane, monophenyl monochloro dimethyl silane anddiphenyl monochloro monomethyl silane, and arylated monoalkoxy alkylsilane such as triphenyl monomethoxy silane, monophenyl dimethyl methoxysilane, and diphenyl monomethoxy monomethyl silane.

Further, the hydrophobic agent forming the alkoxy group as the X groupincludes diazoalkylene such as diazomethane or diazoethane. Thehydrophobic agent forming the OCOR group as the X group includes acetylchloride, propionic acid chloride, or butyric add chloride. Thehydrophobic agent forming the OCONHR group as the X group includes alkylisocyanate such as methyl isocyanate, ethyl isocyanate, propylisocyanate, or butyl isocyanate. Further, in a case where X is hydrogen,hydrogen gas, silane, disilane or lithium aluminum hydride can be usedand in a case where X is fluorine, fluorine gas, xenone fluoride,tetrafluoro silicon, and fluoro alkane such as mono(di, tri ortetra)fluoromethane can be used.

The fine diamond particle film having pores are prepared by coating anddrying the aqueous dispersion thereof on a single crystal siliconsubstrate drawn with a circuit or a glass substrate drawn with a circuitor a conductive film. The fine diamond particle film may be treateddirectly with the hydrophobic agent according to the invention describedabove, or the fine diamond particle film may be strengthened byinterparticle crosslinking using hexachlorodisiloxane,1,3-dichlorotetramethyl disiloxane or dichlorodimethyl silane, followedby hydrophobic treatment. The hydrophobic treating method includes, forexample, a method of dipping the fine diamond particle film coated on asubstrate in a solution of a hydrophobic agent, a method of coating thesolution of a hydrophobic agent on the film, a method of particulatingand spraying a treating solution of the invention on the film, a methodof vaporizing a hydrophobic agent under heating or at an ambienttemperature and reacting the same alone or being diluted with a solvent,or a method of reacting in a plasma atmosphere in a case of a gaseoussubstance such as hydrogen or fluorine.

Sulfoxyl groups or carboxyl groups may sometimes be present on thesurface of the fine diamond particles used in the invention as describedabove. In this case, at least one member of the group consisting ofcalcium, strontium, barium, mercury, silver, lead and radium may also bebonded to the groups. The method of containing the metals into the lowdielectric constant film may be a known method. That is, it includes amethod of forming a fine diamond particle film having pores, thenselecting a water soluble salt such as the hydroxide, hydrogen chlorideor nitride of the metal and dissolving the same in water, impregnatingthe solution into the pores of the fine diamond particle film, bondingthe metal with the carboxyl groups and/or sulfonic acid groups bonded tothe surface of the fine diamond particles to insolubilize the metal andthen water washing and drying the same, or a method of adding thediluted metal salt solution to a dispersion liquid of fine diamondparticles. In a case of conducting the metal salt treatment and thehydrophobic agent treatment together, while any one of them may beconducted previously, a method of conducting the former previously iseasy for the treatment. Combination of the metal salt treatment and thehydrophobic agent treatment together provides the effects of both ofthem, thereby further improving the insulation resistance and thedielectric breakdown voltage.

The invention also includes an electronic part having the low dielectricconstant film described above as a constituent element. As theelectronic part, a semiconductor integrated circuit of high integrationdegree and high speed operation type is most suitable, but it may alsobe a usual semiconductor device or micro machine, or a usual capacitorhaving the low dielectric constant film containing the metal and finediamond particles and comprising pores (fine porous diamond particlefilm).

The fine diamond particles used in the invention are preferably solidparticles with a particle size of from 1 nm to 1000 nm and purified to apurity of 95% or higher. Further, the porosity of the low dielectricconstant film of the invention is preferably from 40% to 80%. In a casewhere it is 40% or less, the dielectric constant increases to 3 or moremainly in a case where the distribution of the particle size of the finediamond particles is broad, which is not preferred. Further, in a casewhere it is 80% or more, a sufficient mechanical strength cannot beobtained, which is insufficient for practical use.

Since the fine diamond particle film of the invention has pores, thesurface is naturally rough and, accordingly, it is preferably densified.For this purpose, a known method such as an SOG (Spin on Glass) method,an SG (Silicate Glass) film method, a BPSG (Boron Phosphate SG) filmmethod or a plasma CVD method, or a method of coating a dispersionliquid of fine diamond particles of 5 nm or less, etc. can be used.

The present inventors have made an earnest study on the reinforcingagent for the fine diamond particle film with an aim of improving theelectric characteristics and, as a result, have developed a lowdielectric constant film having at least fine diamond particles andpores, characterized by a reinforcing treatment of crosslinking finediamond particles to each other, by treating the surface of the finediamond particles with at least one member of the substances at leastrepresented by the following general formula (a), thereby obtaining aremarkable improvement.

(a) General formula: XnR₃-nSi(OSi)mR₃-nXn

(in which n=1 or 2, m=an integer of 0 to 3, X represents halogen group,C₁ to C₆ alkoxy group or phenoxy group, and R represents C₁ to C₆ alkylgroup).

Further, a low dielectric constant film having a sufficient strength andsatisfactory electric characteristics could be obtained by treating thesurface of the fine diamond particles not only with the substancerepresented by the above general formula (a) alone, but also with mixedsubstances of at least one of the substances represented by thefollowing general formula (b) and the substance represented by (a)described above.

(b) Substance represented by general formula: X₃Si(OSi)mX₃

(where m=integer of 0 to 3, X represents halogen group, C₁ to C₆ alkoxygroup or phenoxy group).

The method of treating the fine diamond particle film includes, forexample, a method of dipping in a liquid containing at least thecompound of the general formula (a) and/or (b) (hereinafter referred toas a reinforcing agent), a method of coating a liquid containing thereinforcing agent on the film, a method of spraying a liquid containingthe substance used in the invention on the film, or a method oftreatment by exposing the film to the reinforcing agent as alone orbeing diluted with a solvent as vapor under heating or at an ambienttemperature.

In a case of mixing the compound of the general formula (a) and thecompound of the general formula (b), while (a) and (b) may be from 2:98to 98:2 by weight ratio, it is more preferred that they are at 70:30 to10:90. The weight ratio is based on a mixed weight ratio in a liquidstate before treating the surface of the fine diamond particles. In acase of treatment in a gas state, it is necessary to take the vaporpressure of each substance at a treating temperature into consideration.Hexachlorodisiloxane has higher reactivity than hexamethoxydisiloxane tothe hydroxy group. However, the former releases hydrogen chloride andthe latter releases methanol as a by-product. In a case of forming thelow dielectric constant film of the invention in the course ofmanufacturing a semiconductor circuit, since chlorine ions may sometimesgive undesired effects, the latter is preferred as the treating agent.However, in a circumstance where chlorine ions are removed sufficiently,the former is used. Accordingly, in a case of using the former and thelatter in admixture, the mixing ratio can be determined optionally inaccordance with the situation of the processes for manufacturing varioussemiconductor circuits.

In the above general formula (a) and/or (b), X is at least one halogengroup selected from the group consisting of fluorine, chlorine, bromine,and iodine, or alkoxy group having C₁ to C₆ alkyl or phenoxy group, R isC₁ to C₆ alkyl group. In a case where C is more than 6 both for thealkoxy group and the alkyl group, the reaction rate with the hydroxygroup is lowered, which is not preferred. Further, the phenoxy group(C₆) has reactivity and can be used in the invention. The criterion forselecting either the halogen group or the alkoxy group as X can bedetermined in view of the above-described reactivity and the chlorineion removing circumstance.

Then, in the above general formula (a) and/or (b), in a case where mexceeds 3, the siloxane chain is lengthened to increase the viscosity,thereby making it difficult for impregnation between fine diamondparticles in a case of treatment in the liquid state, which is notpreferred. Further, also in a case of treatment with vapors of thesiloxane compound, the boiling point is increased when m exceeds 3,which is not preferred. Accordingly, a case where m is 1, that is, adisiloxane compound is most preferred.

In the above general formula (a) and/or (b), it is most preferred that Xis at least one member selected from the group consisting of reactivechlorine group, methoxy group or ethoxy group and R is a hydrophobicmethyl group or ethyl group. In addition, it is preferred that m is 1,i.e., a disiloxane compound and further that n is 1 or 2, i.e., two orfour chlorine groups or alkoxy groups such as methoxy groups or ethoxygroups or four or two methyl groups or ethyl groups.

The fine diamond particle film having pores of the invention is formedon a semiconductor substrate such as a single crystal or polycrystalsilicon substrate, a compound semiconductor substrate, a quartzsubstrate, a ceramic substrate, and a glass substrate, or on aintermediate product substrate for manufacturing semiconductor formedwith various circuits. A colloidal solution of the fine diamond particleis coated on the surface of the substrate after the hydrophilictreatment by oxidation.

In addition to the treatment for the film per se deposited by coatingthe colloidal solution of the fine diamond particles as described abovewith the compound of the above general formula (a) and/or (b) of theinvention, it may be sometimes necessary to improve the adhesion betweenthe substrate and the film. In this case, the adhesion between thesubstrate and the fine diamond particle film can be improved also byapplying a pretreatment with the compound of the above general formula(a) and/or (b), among all one or mixture of hexachlorodisiloxane andhexamethoxydisiloxane between the hydrophilic treatment and the coating.In this case, treatment such as drying and heating may optionally beapplied for sufficient reaction.

In the invention, in a case where X is C₁ to C₆ alkoxy group or phenoxygroup in the general formula (b): X₃Si(OSi)mX₃, it may be used as atreating agent without mixing with the substance (a). This substance canreact with hydroxy groups on the surface of fine diamond particles at aroom temperature or by heating to conduct crosslinking between the fineparticles.

In a case where hydroxy groups or silanol groups such as thehexachlorodisiloxane residue remain on the surface of the fine diamondparticles after reinforcement formed on the substrate, they may be madehydrophobic by treating with hexamethyl disilazane, monomethoxy silane,monochloro silane, etc.

Since sulfuric add or nitric add is sometimes used in the purifying stepfor the fine diamond particles used in the invention, sulfonic groups orcarboxy groups may be formed on the surface. In this case, at least onemetal ions of the group consisting of calcium, strontium, barium,mercury, silver, lead or radium may be bonded to the groups. The methodof treating the low dielectric constant film with the metal ionsincludes, for example, a method of forming a fine diamond particle filmhaving pores, then selecting a water soluble salt such as a hydride,hydrogen chloride or nitrate of the metal and dissolving the metal inwater, impregnating the solution into the pores of the fine diamondparticle film and bonding the same with the carboxy groups and/orsulfonic groups bonded to the surface of the fine diamond particles, oradding the solution of the metal salt to the dispersion liquid of thefine diamond particles. In this case, for removing unnecessary metalsalts, sufficient water washing is applied followed by drying. In a caseof conducting the metal salt treatment and the fine particle bondingtreatment together, any of them may be conducted previously butconduction of the former previously is easy for treatment.

Further, combination of the metal salt treatment and the hydrophobicagent treatment with hexamethyl disilazane or the like described aboveprovides the effect of both of them, thereby further improving theinsulation resistance and dielectric breakdown voltage.

The fine diamond particles used in the invention are preferably solidparticles with the particle size of from 1 nm to 1000 nm and purified toa purity of 95% or higher. Further, the porosity of the low dielectricconstant film of the invention is preferably from 40% to 80%. In a casewhere it is 40% or less, the dielectric constant increases to 3 or moremainly in a case where the distribution of the particle size of the finediamond particles is broad, which is not preferred. Further, in a casewhere it is 80% or more, no mechanical strength can be obtained, whichis insufficient for practical use.

For preparing the colloid of the fine diamond particles, while anaqueous medium is generally used, it is preferred that the fine diamondparticles in the dispersion medium are dispersed as primary particles ofthe particle size described above, but they can also be used whenagglomerated to about 30 nm to 1000 nm in appearance to form secondaryparticles. For dispersion, a known fine particle dispersant or knownviscosity modifier may also be used within a range not deteriorating thephysical properties such as the dielectric constant, the electricresistance value, and the dielectric breakdown voltage.

Since the fine diamond particle film of the invention has pores, thesurface is naturally rough and, accordingly, it is preferably densified.For this purpose, a known method such as an SOG (Spin on Glass) method,an SG (Silicate Glass) film method, a BPSG (Boron Phosphate SG) filmmethod or a plasma CVD method, or a method of coating a dispersionliquid of fine diamond particles of 5 nm or less, etc. can be used

The temperature for treating the deposited film formed by coating thecolloidal solution of the fine diamond particles with the compoundcontaining at least the compound of the above general formula (a) and/or(b) is conducted in a range from a room temperature to 400° C. Whiledepending on the boiling point of the solvent used for diluting thecompound, it is preferably treated at a temperature between about 50° C.to 150° C. and reacted simultaneously. Further, the deposited film ofthe fine diamond particles may be treated at a room temperature with avapor or liquid containing the compound and then heated and reacted at atemperature between about 40° C. and 400° C., preferably between about50° C. and 150° C.

The invention also includes an electronic part having the low dielectricconstant film described above as a constituent element. As theelectronic part, a multilayer winning type semiconductor integratedcircuit of high integration degree and high speed operation type is mostsuitable but it may also be a usual semiconductor device or micromachine, or a usual capacitor having a low dielectric constant film ofthe invention comprising fine diamond particles and pores (fine porousdiamond particle film).

Effect of the Invention

In the fine porous diamond particle film applied with the insolubilizingtreatment with metal salt according to the invention, the insulationresistance has been improved by 10 to 20 times and the dielectricbreakdown voltage has also been improved by about three times thanusual. Further, also the specific dielectric constant as the mostprominent feature of the fine porous diamond particle film is unchangedfrom 2.0 before and after the treatment or lowered to about 1.8 and thefunction as the low dielectric constant film is sufficiently maintained.

Further, in the fine porous diamond particle film treated with acompound having the general formula —X group which is more hydrophobicthan the hydroxyl group of the invention, the insulation resistance hasbeen improved by 100 times or more and the dielectric breakdown voltagehas also been improved by 3.5 times or more than those in usual, toreach a practical level. Further, the specific dielectric constant whichis a most prominent feature of the fine porous diamond particle film isunchanged as 2.1 before and after the treatment or lowered to about 1.9and the function as the low dielectric constant film is sufficientlymaintained. Further in a case where sulfonic groups or carboxy groupsare present on the surface of the fine diamond particles, furtherlowering of leak current and increase of the dielectric breakdownvoltage could be obtained by combination with the treatment with themetal salt such as barium chloride. Further, diamond is known as amaterial of good heat conductivity, and the heat conductivity is notdeteriorated even when pores are formed compared with the existent SOGfilm.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing current-voltage characteristics before andafter barium treatment of a fine porous diamond particle film of theinvention. Values in the parentheses show specific dielectric constants.

FIG. 2 is a graph showing the current-voltage characteristics of a fineporous diamond particle film according to the invention before and aftera hydrophobic treatment.

FIG. 3 is a graph showing the current-voltage characteristics of fineporous diamond particle film of Example 1 of the invention (symbol: ▪)and a low dielectric film of Comparative Example 1 (symbol: □).

FIG. 4 is a graph showing the current-voltage characteristics of the adielectric constant film obtained in Example 2 of a fine porous diamondparticle film of the invention (symbol: ▪)

BEST MODES FOR CARRYING OUT THE INVENTION

Examples of the present invention are to be described below but theinvention is not limited only to the examples.

Example 1

<Preparation of Colloidal Solution>

In pure water in a beaker made of quartz, 5% by weight of purified finediamond particles and 1% by weight of polyethylene glycol 600 werecharged and the beaker was dipped in an ultasonic wave tank andsufficiently dispersed for one hour to obtain a gray viscous dispersionliquid.

<Spin Coating Step>

A thoroughly cleaned silicon substrate was placed on a spindle of a spincoater, the colloidal solution described above was poured downward andthe substrate was rotated at 1500 rpm to uniformly coat the same by acentrifugal force.

<Drying Step>

The silicon substrate coated with a liquid of fine diamond particles wasair-dried to form a film and then placed on a hot plate at 300° C. anddried for one hour.

<Reinforcing Treatment for Film Structure>

The silicon substrate with the fine diamond particle film was placed ina vessel and tightly dosed and put to interparticle crosslinking byexposure to a vapor of 1% hexachlorodisiloxane dissolved indichloromethane at an ambient temperature for one hour and then furtherapplied with on overheating treatment at 300° C. for one hour.

<Metal Salt Treatment>

Then, the substrate with the film was dipped in 1% barium hydroxidesolution at an ambient temperature for one hour, after thorough cleaningby downward pouring of pure water, dipped in pure water at an ambienttemperature for one hour, and a purified water was further poureddownward for sufficient cleaning, followed by drying at 100° C. for onehour.

<Measurement of Current-Voltage Characteristic>

A mercury electrode was placed on the film in an atmospheric air, and avoltage was applied between it and a silicon substrate to measure thevoltage, the current value and the dielectric breakdown voltage, whichwere divided by a previous measured film thickness to calculate theelectrolysis intensity.

FIG. 1 shows the property of the film at 540 nm thickness obtained inExample 1. In the fine porous diamond particle film treated with bariumhydroxide, the dielectric breakdown voltage was improved by three timesor more from 0.32 MV/cm to 1.02 MV/cm compared with the film before thetreatment. While the leak current representing the insulation resistancewas about 1×10⁻⁹ A/cm² showing no difference at 0.01 MV/cm, it wasdecreased by about 20 times from 1×10⁻⁴ A/cm² to 2×10⁻⁵ A/cm² at 0.3MV/cm. Further, the specific dielectric constant was improved from 2.0before the metal salt treatment to 1.8.

Example 2

Experiment was conducted in the same procedures except for conductingthe metal salt treatment with 0.17% calcium hydroxide instead of 1%barium hydroxide in Example 1. The film thickness was 430 nm. As aresult, it has been found that the dielectric breakdown voltage improvedfrom 0.86 MV/cm to 1.05 MV/cm and the leak current at 0.82 MV/cmdecreased from 1×10⁻⁴ A/cm² to 7×10⁻⁵ A/cm² also by treatment withcalcium.

Examples of the invention are to be described below but the invention isnot limited only to the examples.

Example 3

<Preparation of Colloidal Solution>

In pure water in a beaker made of quartz, 5% by weight of purified finediamond particles and 1% by weight of polyethylene glycol 600 werecharged and the beaker was dipped in an ultrasonic wave tank andsufficiently dispersed for one hour to obtain a gray viscous dispersionliquid.

<Spin Coating Step>

A thoroughly cleaned silicon substrate of about 20 mm square appliedwith a hydrophilic surface treatment was placed on a spindle of a spincoater, the colloidal solution described above was poured downward andthe substrate was rotated at 1500 rpm to uniformly coat the same by acentrifugal force.

<Drying Step>

The silicon substrate coated with a liquid of fine diamond particles wasair-dried to form a film and then placed on a hot plate at 300° C. anddried for one hour.

<Reinforcing Treatment for Film Structure>

The silicon substrate with the fine diamond particle film was placed ina tightly dosed vessel and put to inter-particle crosslinking byexposure to a vapor of 1% hexachlorodisiloxane (HCDS) dissolved indichloromethane at an ambient temperature for one hour and then furtherapplied with an overheating treatment at 300° C. for one hour.

<Hydrophobic Treatment>

Then, the substrate with the film was placed in a vessel containing aliquid mixture of 1% hexamethyl disilazane (HMDS)/dichloromethane andtightly closed, and exposed to the vapor at an ambient temperature forone hour to conduct a hydrophobic treatment and, thereafter, furtherapplied with an overheating treatment at 300° C. for one hour.

<Measurement of Current-Voltage Characteristics>

A mercury electrode was placed on a film in an atmospheric air and avoltage was applied between it and a silicon substrate to measure thevoltage, the current value and the dielectric breakdown voltage, whichwere divided with a previously measured film thickness to calculate theelectrolysis intensity.

FIG. 2 shows the current-voltage characteristics of the film at 430 nmthickness obtained in Example 3. In the fine porous diamond particlefilm applied with a hydrophobic treatment, the dielectric breakdownvoltage was improved by about twice from 0.57 MV/cm to 1.03 MV/cm. Theleak current representing the insulative resistance was lowered from1×10⁻⁷ A/cm² to 2×10⁻⁹ A/cm² at a voltage of 0.01 MV/cm and lowered to1/100 from 1×10⁻¹⁵ A/cm² to 1×10⁻⁷ A/cm² at 0.23 MV/cm. Further, thespecific dielectric constant was unchanged as 2.0 before and after thetreatment. As shown by a broken line in FIG. 2, while dielectricbreakdown voltage of 1 MV/cm or more is generally required, theinvention meets the requirement. Further, while 10⁻⁶ A/cm² or less ofthe leak current is required, this could be attained at a voltage of 0.4MV/cm or lower.

Example 4

Experiment was conducted by the same procedures except for treating witha gas of 1% trimethyl monochloro silane/toluene solution instead of 1%hexamethyl disilazane in Example 3. The film thickness was 530 nm. As aresult, by treatment with trimethyl monochloro silane, 1.11 MV/cm whichwas higher than 1 MV/cm was attained for the dielectric breakdownvoltage and 1.1×10−7 A/cm² of the leak current was attained at a voltageof 0.2 MV/cm.

Example 5

<Preparation of Colloidal Solution>

In pure water in a beaker made of quartz, 5% by weight of purified finediamond particles, 0.1% by weight of dimethylamine, and 1% by weight ofpolyethylene glycol with a molecular weight of 5,000,000 were chargedand the beaker was dipped in an ultrasonic wave tank and sufficientlydispersed for one hour to obtain a gray viscous dispersion liquid.

<Spin Coating Step>

A thoroughly cleaned silicon substrate was cut in about 20 mm square,applied with a hydrophilic surface treatment, and then placed on aspindle of a spin coater, the colloidal solution described above waspoured downward and the substrate was rotated at 1500 rpm to uniformlycoat the same by a centrifugal force.

<Drying Step>

The silicon substrate coated with a liquid of fine diamond particles wasair-dried to form a film and then placed on a hot plate at 300° C. anddried for one hour.

<Reinforcing Treatment for Film Structure>

The silicon substrate with the fine diamond particle film was placed ina tightly dosed vessel, put to interparticle permeating sufficiently byexposure to a vapor of 10% dichlorotetramethyl disiloxane (DCTMDS)dissolved in dichloromethane at an ambient temperature for one hour, andthen further applied with an overheating treatment at 300° C. for onehour.

<Measurement of Current-Voltage Characteristics>

A mercury electrode was placed on a film in an atmospheric air and avoltage was applied between it and the silicon substrate to measure thevoltage, the current value, and the dielectric breakdown voltage, whichwere divided with a previously measured film thickness to calculate theelectrolysis intensity.

FIG. 3 shows the current-voltage characteristics of the film at 510 nmthickness obtained in Example 5. In the fine porous diamond particlefilm applied with a DCTMDS treatment, the dielectric breakdown voltagewas improved by 3.5 times or more from 0.57 MV/cm to 2.0 MV/cm(measuring limit) compared with the film obtained in Comparative Example1 to be described later. The leak current representing the insulationresistance was lowered from 1×10⁻⁴ A/cm² to 7×10⁻⁸ A/cm² at a voltage of0.57 MV/cm and lowered to 1×10⁻⁷ A/cm² at 1 MV/cm when compared in thesame manner. Further, the dielectric constant was unchanged as 2.0before and after the treatment. As shown by the broken line in FIG. 3,while 1 MV/cm or higher of the dielectric breakdown voltage and 1×10⁻⁶A/cm² or less of the leak current are generally required, both of themare cleared in the invention, to reach a practical level.

Further, the fine porous diamond particle film in this example had nodisadvantages such as destruction of interparticle bond and maintainedsufficient strength upon measurement by contacting the electriccharacteristic measuring probe or upon finger touch friction.

Example 6

Experiment was conducted in the same procedures except for treatmentwith a gas of a liquid mixture of 1% by weight of DCTMDS and 1% byweight of hexachloro disiloxane instead of 10% DCTMDS in Example 5. As aresult of measurement, the film thickness was 680 nm and the specificdielectric constant was 2.1. A dielectric breakdown voltage of 1.43MV/cm which was higher than 1 MV/cm and a leak current of 2×10⁻⁷ A/cm²which was less than 1×10⁻⁶ A/cm² at a voltage of 1 MV/cm were attained.Further, the fine porous diamond particle film of the example showed nodisadvantages such as destruction of interparticle bond and maintainedsufficient strength even upon finger touch friction.

Comparative Example 1

Experiment was conducted in the same procedures except for treatmentwith a gas of 1% by weight of a hexachlorodisiloxane solution instead of10% by weight of DCTMDS in Example 5. The film thickness was 510 nm. Thefine porous diamond particle film had a dielectric breakdown voltage of0.6 MV/cm and a leak current of 1×10⁻⁴ A/cm² just before and could notmeet the requirement for 1 MV/cm or higher of the dielectric breakdownvoltage and 1×10⁻⁶ A/cm² or less of the leak current as the practicalstranded

INDUSTRIAL APPLICABILITY

According to the invention, a specific dielectric constant of 1.8 hasbeen attained for the first time by using a fine porous diamond particlefilm which is an inorganic low dielectric constant film having high heatresistance and heat conductivity. Further, also the dielectric breakdownvoltage has cleared 1 MV/cm as a practical standard and also the leakcurrent has been about from 10⁻⁸ A/cm² to 10⁻⁹ A/cm² at a practicalvoltage. This enables to manufacture not only multi-layered wiringsemiconductor devices or semiconductor capacitors, as well as other highperformance general-purpose electronic parts such as high performancecapacitors.

According to the invention, a specific dielectric constant of 2.0 hasbeen attained by using a fine porous diamond particle film which is aninorganic low dielectric constant film having high heat resistance andheat conductivity. Further, also the dielectric breakdown voltage hasattained 1 MV/cm as a practical standard and also the leak current hasbeen about from 10⁻⁸ A/cm² to 10⁻⁹ A/cm² at a practical voltage. Thisenables to manufacture not only multi-layered wiring semiconductordevices or semiconductor capacitors, as well as other high performancegeneral-purpose electronic parts such as high performance capacitors andinterwiring insulators.

According to the invention, the specific dielectric constant of 2.0 hasbeen attained by using a fine porous diamond particle film which is aninorganic low dielectric constant film having high heat resistance andheat conductivity. Further, also the dielectric breakdown voltage hasattained 2.0 MV/cm (measuring limit) or higher exceeding 1 MV/cm whichis the practical standard and also the leak current has attained 1×10⁻⁷A/cm² at the practical voltage of 1 MV/cm. This enables to manufacturenot only multi-layered wiring semiconductor devices or semiconductorcapacitors, as well as other high performance general purpose electronicparts such as high performance capacitors and inter-wiring insulators,and can greatly contribute to the development of electronic industryincluding computers.

1. A low dielectric constant film comprising a film comprising at leastfine diamond particles and pores, wherein said low dielectric constantfilm comprises at least one metal selected from the group of metalswhose carbonate salt or a sulfate salt has a solubility of 1 g/100 g orless at an ambient temperature.
 2. The low dielectric constant film ofclaim 1, wherein said metal is at least one member of the groupconsisting of calcium, strontium, barium, mercury, silver, lead andradium.
 3. A low dielectric constant film having at least fine diamondparticles and pores, wherein said low dielectric constant film istreated with an aqueous solution of a salt of at least one metalselected from the group of metals whose carbonate salt or sulfate salthas a solubility of 1 g/100 g or less at an ambient temperature.
 4. Thelow dielectric constant film of claim 3, which is treated with anaqueous solution of a salt of at least one metal of the group consistingof calcium, strontium, barium, mercury, silver, lead and radium.
 5. Anelectronic part comprising a low dielectric constant film according toclaim 1 as at least one constituent element.
 6. A low dielectricconstant film comprising a film comprising at least fine diamondparticles and pores, wherein the surface of said fine diamond particleshas a group of a general formula of —X group which is more hydrophobicthan hydroxyl group instead of hydroxyl group.
 7. The low dielectricconstant film of claim 6, wherein X in said general formula of —X groupis at least one member selected from the group consisting of hydrogen,fluorine, C₁ to C₄ alkoxy group, phenoxy group, o-(m- or p-)alkylphenoxygroup (in which alkyl group is C₁ to C₄ alkyl group), OCOR, OCONRR′,OSiR₃ [in which R and R′ each represents hydrogen, C₁ to C₄ alkyl group,phenyl group or o-(m-or p-)alkylphenyl group].
 8. The low dielectricconstant film of claim 6, wherein X in the general formula of —X groupis OSiR₃ (where R is C₁ to C₄ alkyl group).
 9. An electronic partcontaining said dielectric constant film of claim 6 as at least oneconstituent element.
 10. A method of manufacturing a low dielectricconstant film, said method comprising the step of reacting activehydroxyl groups on the surface of fine diamond particles and ahydrophobic agent.
 11. The method of manufacturing a low dielectricconstant film of claim 10, wherein said hydrophobic agent is at leastone member selected from the group consisting of hexaalkyl disilazane,trialkyl monohalogen silane, triphenyl monohalogen silane, arylatedalkyl monohalogen silane, dialkyl dihalogen silane, trialkyl monomethoxysilane, triphenyl monomethoxy silane, arylated monoalkoxy alkyl silane,dialkyl dimethoxy silane and diazoalkylene.
 12. A low dielectricconstant film comprising a film comprising at least fine diamondparticles and pores, wherein the surface of said fine diamond particlesis treated with at least one single substance of the following (a) or amixture of substances of at least one of (a) and at least one of (b) asdescribed below: (a) a substance represented by the general formula:XnR₃-nSi(OSi)mR₃-nXn (b) a substance represented by the general formula;X₃Si(OSi)mX₃ (where n=1 or 2, m=an integer of 0 to 3, X represents ahalogen group, C₁ to C₆ alkoxy group or phenoxy group, and R representsC₁ to C₆ alkyl group).
 13. The low dielectric constant film of claim 12,wherein X is at least one member selected from the group consisting ofchlorine group, methoxy group and ethoxy group and R represents methylgroup or ethyl group in the general formula (a) and the general formula(b).
 14. The low dielectric constant film of claim 12, wherein m is 1 inthe general formula (a) and the general formula (b).
 15. The lowdielectric constant film of claim 12, wherein n is 1 in the generalformula (a).
 16. The low dielectric constant film of claim 12, whereinsaid substance of the general formula (a) is at least one memberselected from the group consisting of dichloro tetramethyl disiloxane,dimethoxy tetramethyl disiloxane, tetrachloro dimethyl disiloxane andtetramethoxy dimethyl disiloxane, and said substance of the generalformula (b) is at least one member selected from the group consisting ofhexachlorodisiloxane, hexamethoxy disiloxane and hexaethoxy disiloxane.17. The low dielectric constant film of claim 12 wherein the surface ofsaid fine diamond particles is treated with at least one member of thegeneral formula (b) in which X represents a C₁ to C₆ alkoxy group orphenoxy group.
 18. An electronic part comprising the low dielectricconstant film of claim 12 as at least one constituent element.
 19. Amethod of manufacturing a low dielectric constant film of claim 12, saidmethod comprising the step of chemically reacting hydroxyl groups on thesurface of fine diamond particles and at least one single substance of(a) or a mixed substances of at least one of (a) and at least one of (b)described above.
 20. The method of manufacturing a low dielectricconstant film of claim 19, wherein said substance of the general formula(a) is at least one member selected from the group consisting ofdichloro tetramethyl disiloxane, dimethoxy tetramethyl disiloxane,tetrachloro dimethyl disiloxane and tetramethoxy dimethyl disiloxane,and therein said substance of the general formula (b) is at least onemember selected from the group consisting of hexachlordisiloxane,hexamethoxy disiloxane and hexaethoxy disiloxane.